Adjustable cord bracelets are probably the fastest ones you can make. It’s a good technique to use for using up odd beads. Gemstone ones are particularly desirable. Those who are metal allergic will be interested in this method as there are no metal clasps.
Check out this easy and quick tutorial which uses a straw aid to make the knots on either side of the bead(s). The Chinese instructor is Karen Hui who has a Youtube channel as well as an Etsy store called DIYNotion where she sells many handmade cord bracelets as well as supplies. A single mother, she started her business as a way of support and moving forward.